US10749498B2 - Elastic wave device, high-frequency front end circuit, and communication device - Google Patents

Elastic wave device, high-frequency front end circuit, and communication device Download PDF

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US10749498B2
US10749498B2 US16/261,667 US201916261667A US10749498B2 US 10749498 B2 US10749498 B2 US 10749498B2 US 201916261667 A US201916261667 A US 201916261667A US 10749498 B2 US10749498 B2 US 10749498B2
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acoustic
elastic wave
velocity
end region
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US20190158059A1 (en
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Yasumasa TANIGUCHI
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Murata Manufacturing Co Ltd
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Murata Manufacturing Co Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/1457—Transducers having different finger widths
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/56—Modifications of input or output impedances, not otherwise provided for
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
    • H03F3/245—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages with semiconductor devices only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02543—Characteristics of substrate, e.g. cutting angles
    • H03H9/02559—Characteristics of substrate, e.g. cutting angles of lithium niobate or lithium-tantalate substrates
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02637—Details concerning reflective or coupling arrays
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02858—Means for compensation or elimination of undesirable effects of wave front distortion
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02866—Means for compensation or elimination of undesirable effects of bulk wave excitation and reflections
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02881—Means for compensation or elimination of undesirable effects of diffraction of wave beam
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02992—Details of bus bars, contact pads or other electrical connections for finger electrodes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/05—Holders; Supports
    • H03H9/10—Mounting in enclosures
    • H03H9/12—Mounting in enclosures for networks with interaction of optical and acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
    • H03H9/72—Networks using surface acoustic waves
    • H03H9/725—Duplexers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/451—Indexing scheme relating to amplifiers the amplifier being a radio frequency amplifier

Definitions

  • the present invention relates to an elastic wave device that utilizes a piston mode, a high-frequency front end circuit, and a communication device.
  • an elastic wave device that utilizes a piston mode in order to suppress an unwanted wave.
  • Japanese Patent No. 5221616 discloses an example of an elastic wave device that utilizes a piston mode.
  • This elastic wave device includes a crossing region in which a plurality of first electrode fingers and a plurality of second electrode fingers of an IDT electrode are superposed with each other when viewed in an elastic wave propagation direction.
  • the crossing region includes a center region that is located in the center in the direction in which the first and second electrode fingers extend and first and second edge regions that are provided on both sides of the center region in the direction in which the first and second electrode fingers extend.
  • first and second edge regions a dielectric film or a metal film is stacked on the first and second electrode fingers and the electrode width (duty) of the edge regions is increased. Consequently, the acoustic velocity in the first and second edge regions is lower than the acoustic velocity in the center region and in regions outside the first and second edge regions. In this manner, the energy of elastic waves is confined and unwanted waves are suppressed.
  • Preferred embodiments of the present invention provide elastic wave devices, high-frequency front end circuits, and communication devices that effectively confine an elastic wave that is to be utilized and reduce or prevent an unwanted wave.
  • An elastic wave device includes a piezoelectric body and an IDT electrode provided on the piezoelectric body.
  • the IDT electrode includes a first busbar and a second busbar that face each other, a plurality of first electrode fingers including first ends that are connected to the first busbar, and a plurality of second electrode fingers including first ends that are connected to the second busbar and that are interdigitated with the plurality of first electrode fingers.
  • the IDT electrode includes a first end region that includes one end of the IDT electrode in an elastic wave propagation direction, a second end region that includes another end of the IDT electrode in the elastic wave propagation direction, and an inner region that is located inside from the first end region and the second end region in the elastic wave propagation direction, and includes a crossing region that is a portion of the IDT electrode in which the first electrode fingers and the second electrode fingers are superposed with each other in the elastic wave propagation direction.
  • the IDT electrode in the crossing region in at least the inner region, includes a center region that is centrally located in the length direction and a first low-acoustic-velocity region and a second low-acoustic-velocity region that are disposed on both sides of the center region in the length direction and in which an acoustic velocity is lower than in the center region.
  • the IDT electrode includes a first high-acoustic-velocity region between the first busbar and the first low-acoustic-velocity region and in which an acoustic velocity is higher than in the center region and a second high-acoustic-velocity region between the second busbar and the second low-acoustic-velocity region and in which an acoustic velocity is higher than in the center region.
  • the mass of the IDT electrode in the crossing region in the first end region and/or the mass of the IDT electrode in the crossing region in the second end region is smaller than the mass of the IDT electrode in the crossing region in the inner region.
  • the IDT electrode includes the center region, the first low-acoustic-velocity region, and the second low-acoustic-velocity region in the crossing region in the inner region, the first end region, and the second end region.
  • the duty in the center region in the first end region and/or the second end region is smaller than the duty in the center region in the inner region (i.e., the duty of the electrode fingers of the IDT electrode, referred to hereinafter as simply “duty”). In this case, an unwanted wave is further reduced or prevented.
  • the duty close to the first low-acoustic-velocity region and close to the second low-acoustic-velocity region in the center region in the first end region and/or the second end region is smaller than the duty in the center region in the inner region. In this case, an unwanted wave is further reduced or prevented.
  • the duty in the center region in the first end region and/or the second end region gradually decreases in a direction toward to the outside in the elastic wave propagation direction. In this case, an unwanted wave is further reduced or prevented, and a Rayleigh wave is less likely to leak.
  • the duty in the first low-acoustic-velocity region and the duty in the second low-acoustic-velocity region in the first end region and the second end region are larger than the duties in the center region in the first end region and the second end region.
  • the acoustic velocity in the first and second low-acoustic-velocity regions is able to be reduced.
  • an additional mass film is stacked on a plurality of portions of the first end region and second end region located in first low-acoustic-velocity region and the second low-acoustic-velocity region.
  • the acoustic velocity in the first and second low-acoustic-velocity regions is able to be reduced.
  • the IDT electrode includes a plurality of first dummy electrode fingers that include first ends connected to the first busbar, that face the plurality of second electrode fingers with gaps therebetween, and that are provided in the first end region and/or the second end region, and a plurality of second dummy electrode fingers that include first ends connected to the second busbar, that face the plurality of first electrode fingers with gaps therebetween, and that are provided in the first end region and/or the second end region, and the first low-acoustic-velocity region and the second low-acoustic-velocity region are not arranged in the first end region and the second end region. In this case, an unwanted wave is further reduced or prevented.
  • the gaps between the plurality of first electrode fingers and the plurality of second dummy electrode fingers are superposed with the crossing region in the inner region when viewed in the elastic wave propagation direction, and the gaps between the plurality of second electrode fingers and the plurality of first dummy electrode fingers are superposed with the crossing region in the inner region when viewed in the elastic wave propagation direction.
  • an unwanted wave is more effectively reduced or prevented.
  • the mass of the IDT electrode in the crossing region in the first end region and the mass of the IDT electrode in the crossing region in the second end region are smaller than the mass of the IDT electrode in the crossing region in the inner region
  • the first dummy electrode fingers and the second dummy electrode fingers are provided in the first end region and the second end region
  • the plurality of first dummy electrode fingers have different lengths from each other in the first end region
  • the plurality of first dummy electrode fingers have different lengths from each other in the second end region
  • the plurality of second dummy electrode fingers have different lengths from each other in the first end region
  • the plurality of second dummy electrode fingers have different lengths from each other in the second end region
  • the lengths of the plurality of first dummy electrode fingers and the lengths of the second dummy electrode fingers increase the closer the dummy electrode fingers are to the outside in the elastic wave propagation direction. In this case, an unwanted wave is further reduced or prevented.
  • the mass of the IDT electrode in the crossing region in the first end region and the mass of the IDT electrode in the crossing region in the second end region are smaller than the mass of the IDT electrode in the crossing region in the inner region. In this case, an unwanted wave is further reduced or prevented.
  • the area of the first end region and the area of the second end region each occupy about 2% to about 5% of the area of the IDT electrode. In this case, an unwanted wave is effectively reduced or prevented.
  • a Rayleigh wave is utilized.
  • preferred embodiments of the present invention are particularly suitably applied.
  • a high-frequency front end circuit includes an elastic wave device according to a preferred embodiment of the present invention and a power amplifier.
  • a communication device includes a high-frequency front end circuit according to a preferred embodiment of the present invention and an RF signal processing circuit.
  • elastic wave devices, high-frequency front end circuits, and communication devices that effectively confine an elastic wave that is to be utilized and that reduce or prevent an unwanted wave are able to be provided.
  • FIG. 1 is a schematic plan view of an elastic wave device according to a first preferred embodiment of the present invention.
  • FIG. 2 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in the first preferred embodiment of the present invention.
  • FIG. 3 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a comparative example.
  • FIG. 4 is a diagram illustrating an impedance-frequency characteristic of an elastic wave device of the comparative example.
  • FIG. 5 is a diagram illustrating return loss of the elastic wave device of the comparative example.
  • FIG. 6 is a diagram illustrating the return loss of the elastic wave device according to the first preferred embodiment of the present invention.
  • FIG. 7 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a second preferred embodiment of the present invention.
  • FIG. 8 is a diagram illustrating the return loss of an elastic wave device according to the second preferred embodiment of the present invention.
  • FIG. 9 is a schematic plan view of an elastic wave device according to a third preferred embodiment of the present invention.
  • FIG. 10 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in the third preferred embodiment of the present invention.
  • FIG. 11 is a diagram illustrating the return loss of an elastic wave device according to the third preferred embodiment of the present invention.
  • FIG. 12 is a schematic plan view of an elastic wave device according to a fourth preferred embodiment of the present invention.
  • FIG. 13 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in the fourth preferred embodiment of the present invention.
  • FIG. 14 is a diagram illustrating the return loss of an elastic wave device according to the fourth preferred embodiment of the present invention.
  • FIG. 15 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a fifth preferred embodiment of the present invention.
  • FIG. 16 is a diagram illustrating the return loss of an elastic wave device according to the fifth preferred embodiment of the present invention.
  • FIG. 17 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a sixth preferred embodiment of the present invention.
  • FIG. 18 is a diagram illustrating the impedance-frequency characteristics of elastic wave devices of the sixth preferred embodiment of the present invention and a comparative example.
  • FIG. 19 is an enlargement of FIG. 18 .
  • FIG. 20 is a diagram illustrating the return losses of elastic wave devices according to the sixth preferred embodiment of the present invention and the comparative example.
  • FIG. 21 is a diagram illustrating the configurations of a communication device and a high-frequency front end circuit according to preferred embodiments of the present invention.
  • FIG. 1 is a schematic plan view of an elastic wave device according to a first preferred embodiment of the present invention.
  • An elastic wave device 1 includes a piezoelectric substrate 2 as a piezoelectric body.
  • the piezoelectric substrate 2 is preferably made of, for example, 128.5° Y-cut X-propagation LiNbO 3 .
  • the cut angle of the piezoelectric substrate 2 is not limited to this example.
  • the material of the piezoelectric substrate 2 is not limited to the above example, and may instead be a piezoelectric single crystal, such as LiTaO 3 or a suitable piezoelectric ceramic, for example.
  • the IDT electrode 3 is provided on the piezoelectric substrate 2 .
  • the IDT electrode 3 includes first and second busbars 3 a 1 and 3 b 1 and a plurality of first and second electrode fingers 3 a 2 and 3 b 2 .
  • the first and second busbars 3 a 1 and 3 b 1 face each other.
  • First ends of the plurality of first electrode fingers 3 a 2 are connected to the first busbar 3 a 1 .
  • First ends of the plurality of second electrode fingers 3 b 2 are connected to the second busbar 3 b 1 .
  • the plurality of first and second electrode fingers 3 a 2 and 3 b 2 are interdigitated with each other.
  • the first and second busbars 3 a 1 and 3 b 1 include a lower layer electrode that is stacked on the piezoelectric substrate 2 and an upper layer electrode 3 c that is stacked on the lower layer electrode. Electrical resistance is able to be reduced in this manner.
  • the first and second busbars 3 a 1 and 3 b 1 do not have to include the upper layer electrode 3 c.
  • an elastic wave is excited by applying an alternating-current voltage to the IDT electrode 3 .
  • the elastic wave device 1 preferably utilizes Rayleigh waves, for example. In this case, preferred embodiments of the present invention are particularly suitably applied.
  • Reflectors 4 a and 4 b are provided on both sides of the IDT electrode 3 in an elastic wave propagation direction.
  • the plurality of first and second electrode fingers 3 a 2 and 3 b 2 include 100 pairs of electrode fingers, and the pluralities of electrode fingers of the reflectors 4 a and 4 b each include 21 electrode fingers.
  • the IDT electrode 3 and the reflectors 4 a and 4 b are illustrated in a schematic manner, and the number of pairs of electrode fingers and the numbers of electrode fingers are different from those described above. The same also applies to FIGS. 9 and 12 described later.
  • the IDT electrode 3 includes a first end region C 1 that includes one end of the IDT electrode 3 in the elastic wave propagation direction and a second end region C 2 that includes the other end of the IDT electrode 3 in the elastic wave propagation direction.
  • the IDT electrode 3 includes an inner region D that is located farther toward the inside than the first and second end regions C 1 and C 2 in the elastic wave propagation direction.
  • first and second end regions C 1 and C 2 each include two pairs of the first and second electrode fingers 3 a 2 and 3 b 2 .
  • the first end region C 1 includes five electrode fingers from the electrode fingers located closest to the reflector 4 a.
  • the second end region C 2 includes five electrode fingers from the electrode fingers located closest to the reflector 4 b.
  • the areas of the first and second end regions C 1 and C 2 each occupy, for example, about 2% of the IDT electrode 3 . It is sufficient that the areas of the first and second end regions C 1 and C 2 each occupy about 20% or less of the area of the IDT electrode 3 .
  • the IDT electrode 3 includes a crossing region A in which the first electrode fingers 3 a 2 and the second electrode fingers 3 b 2 are superposed with each other when viewed in the elastic wave propagation direction.
  • a direction in which the first and second electrode fingers 3 a 2 and 3 b 2 extend is referred to as a length direction.
  • the crossing region A includes a center region Aa located in the center in the length direction.
  • the crossing region A includes first and second low-acoustic-velocity regions Ab 1 and Ab 2 on both sides of the center region Aa in the length direction.
  • the center region Aa is disposed between the first low-acoustic-velocity region Ab 1 and the second low-acoustic-velocity region Ab 2 in the length direction.
  • the region between the first low-acoustic-velocity region Ab 1 and the second low-acoustic-velocity region Ab 2 is not included in the first low-acoustic-velocity region Ab 1 and the second low-acoustic-velocity region Ab 2 .
  • An acoustic velocity V 2 in the first and second low-acoustic-velocity regions Ab 1 and Ab 2 is lower than an acoustic velocity V 1 in the center region Aa.
  • the IDT electrode 3 includes a first high-acoustic-velocity region B 1 between the first busbar 3 a 1 and the first low-acoustic-velocity region Ab 1 .
  • An acoustic velocity V 3 in the first high-acoustic-velocity region B 1 is higher than the acoustic velocity V 1 in the center region Aa.
  • the IDT electrode 3 includes a second high-acoustic-velocity region B 2 between the second busbar 3 b 1 and the second low-acoustic-velocity region Ab 2 .
  • the acoustic velocity V 3 in the second high-acoustic-velocity region B 2 is higher than the acoustic velocity V 1 in the center region Aa.
  • FIG. 1 The relationship between the acoustic velocities V 1 , V 2 , and V 3 is illustrated in FIG. 1 .
  • a higher acoustic velocity is illustrated as being located farther toward the right side in FIG. 1 .
  • ⁇ represents the wavelength of an elastic wave defined by the electrode finger pitch of the IDT electrode 3 .
  • the dimension of each of the first and second high-acoustic-velocity regions B 1 and B 2 in the length direction is preferably about 2 ⁇ , for example.
  • the dimension of each of the first and second high-acoustic-velocity regions B 1 and B 2 in the length direction is not limited to this example.
  • the crossing region A includes the center region Aa and the first and second low-acoustic-velocity regions Ab 1 and Ab 2 in the inner region D and the first and second end regions C 1 and C 2 . It is sufficient that the crossing region A include the center region Aa and the first and second low-acoustic-velocity regions Ab 1 and Ab 2 in at least the inner region D.
  • FIG. 2 is an enlarged plan view of the vicinity of the first end region of the IDT electrode in the first preferred embodiment.
  • the duty of the first low-acoustic-velocity region Ab 1 is larger than the duty of the center region Aa in the IDT electrode 3 . Consequently, the acoustic velocity in the first low-acoustic-velocity region Ab 1 is able to be reduced.
  • additional mass films 5 are stacked on the portions of the plurality of first and second electrode fingers 3 a 2 and 3 b 2 that are located in the first low-acoustic-velocity region Ab 1 . Consequently, the acoustic velocity in the first low-acoustic-velocity region Ab 1 is able to be further reduced.
  • the additional mass films 5 are preferably made of a suitable metal.
  • the additional mass films 5 may instead be made of a dielectric or other suitable material.
  • the additional mass films 5 may have a strip shape that extends in the elastic wave propagation direction and the additional mass films 5 on adjacent electrode fingers may be integrated with each other.
  • the configuration used to reduce the acoustic velocity in the first low-acoustic-velocity region Ab 1 is not particularly limited.
  • the additional mass films 5 do not have to be provided.
  • the additional mass films 5 may be provided and the duty of the first low-acoustic-velocity region Ab 1 and the duty of the center region Aa may be the same or substantially the same as each other.
  • the plurality of first and second electrode fingers 3 a 2 and 3 b 2 are configured in the second low-acoustic-velocity region in the same or substantially the same manner as in the first low-acoustic-velocity region Ab 1 .
  • the duty of the center region Aa in the first end region C 1 is smaller than the duty of the center region Aa in the inner region D. More specifically, the duty across the entire or substantially the entire center region Aa in the first end region C 1 is smaller than the duty of the center region Aa in the inner region D. Therefore, the mass of the IDT electrode 3 in the crossing region in the first end region C 1 is smaller than the mass of the IDT electrode 3 in the crossing region in the inner region D. In other words, the mass of the electrode fingers in the crossing region in the first end region C 1 is smaller than the mass of the electrode fingers in the crossing region in the inner region D.
  • the second end region of the IDT electrode 3 is configured in the same or substantially the same manner as the first end region C 1 .
  • the duty of the center region Aa in the second end region is smaller than the duty of the center region Aa in the inner region D. Therefore, the mass of the electrode fingers in the crossing region in the second end region is smaller than the mass of the electrode fingers in the crossing region in the inner region D.
  • the duty of the center region Aa in the first end region C 1 and the second end region is not particularly limited, but is preferably, for example, about 0.4 in the present preferred embodiment.
  • the duty of the center region Aa in the inner region D is not particularly limited but is preferably, for example, about 0.5 in the present preferred embodiment.
  • the mass of the electrode fingers in the crossing region A in the first and second end regions C 1 and C 2 is smaller than the mass of the electrode fingers in the crossing region A in the inner region D. Consequently, the elastic wave that is utilized is able to be effectively confined and an unwanted wave is reduced or prevented. This will be described below by comparing the present preferred embodiment and a comparative example.
  • an elastic wave device of a comparative example differs from the first preferred embodiment in that the duty of a center region Aa in a first end region C 1 and a second end region of an IDT electrode 103 and the duty of the center region Aa in an inner region D of the IDT electrode 103 are the same as each other.
  • the mass of the electrode fingers in the crossing region in the first end region C 1 and the second end region of the IDT electrode 103 is the same as the mass of the electrode fingers in the crossing region in the inner region D.
  • FIG. 4 is a diagram illustrating an impedance-frequency characteristic of the elastic wave device of the comparative example.
  • FIG. 5 is a diagram illustrating return loss of the elastic wave device of the comparative example.
  • FIG. 6 is a diagram illustrating the return loss of the elastic wave device according to the first preferred embodiment. Arrows X in FIGS. 4 to 6 indicate the frequency at which a shear horizontal wave is generated. This is also true for drawings illustrating impedance-frequency characteristics and drawings illustrating return losses referred to later.
  • a shear horizontal wave which is an unwanted wave, is generated between a resonant frequency and an anti-resonant frequency in the elastic wave device of the comparative example.
  • the return loss of the shear horizontal wave is about 2.05 dB in the comparative example.
  • the return loss of the shear horizontal wave is about 1.8 dB in the first preferred embodiment and it is clear that the return loss is improved compared with the comparative example.
  • the mass of the electrode fingers in the first and second end regions is small.
  • the shear horizontal wave is effectively allowed to leak in the thickness direction of the piezoelectric substrate.
  • the energy density of a Rayleigh wave tends to be higher in the vicinity of the center of an IDT electrode. Therefore, even though the mass of the electrode fingers is smaller in the first and second end regions, it is difficult for the Rayleigh waves to leak out.
  • the elastic wave that is utilized is able to be effectively confined and unwanted waves are reduced or prevented.
  • the mass of the electrode fingers in the crossing region in the first end region or the mass of the electrode fingers in the crossing region in the second end region are smaller than the mass of the electrode fingers in the crossing region in the inner region. This is also true in the second to sixth preferred embodiments described below. However, it is preferable that the mass of the electrode fingers in the crossing region in the first end region and the mass of the electrode fingers in the crossing region in the second end region is smaller than the mass of the electrode fingers in the crossing region in the inner region. In this manner, unwanted waves are further reduced or prevented.
  • the piezoelectric body is a piezoelectric substrate, but the piezoelectric body may instead be a piezoelectric thin film.
  • a low-acoustic-velocity film may be provided on the surface of a piezoelectric thin film on the opposite side from a surface of the piezoelectric thin film on which an IDT electrode is provided.
  • a high-acoustic-velocity member may be provided on a surface of the low-acoustic-velocity film that is on the opposite side from the piezoelectric thin film.
  • the low-acoustic-velocity film is a film in which the acoustic velocity of a propagating bulk wave is lower than the acoustic velocity of an elastic wave propagating along the piezoelectric thin film.
  • the low-acoustic-velocity film is preferably made of, for example, a material including a main component that is a compound obtained by adding fluorine, carbon, or boron to glass, silicon oxynitride, tantalum oxide, or silicon oxide. It is sufficient that the material of the low-acoustic-velocity film is a material having a relatively low acoustic velocity.
  • the high-acoustic-velocity member is a member in which the acoustic velocity of a propagating bulk wave is higher than the acoustic velocity of an elastic wave propagating along the piezoelectric thin film.
  • the high-acoustic-velocity member is preferably made of, for example, a material having aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, a DLC film or diamond as a main component.
  • the material of the high-acoustic-velocity member be a material having a relatively high acoustic velocity.
  • the high-acoustic-velocity member may be a high-acoustic-velocity film or may be a high-acoustic-velocity substrate.
  • a low-acoustic-velocity film and a high-acoustic-velocity member are provided in this manner, the energy of elastic waves is able to be effectively confined.
  • FIG. 7 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a second preferred embodiment of the present invention.
  • An elastic wave device differs from the first preferred embodiment in that the duty of a center region Aa gradually changes in a first end region C 11 and a second end region of an IDT electrode 13 .
  • the areas of the first end region C 11 and the second end region are different from those in the first preferred embodiment.
  • the elastic wave device according to the second preferred embodiment has the same or substantially the same configuration as the elastic wave device 1 of the first preferred embodiment.
  • the duty in the center region Aa in an inner region D 10 is preferably, for example, about 0.5 similarly to as in the first preferred embodiment.
  • the first end region C 11 and the second end region each include eleven electrode fingers.
  • the areas of the first end region C 11 and the second end region each preferably occupy, for example, about 5% of the area of the IDT electrode 13 .
  • the areas of the first end region C 11 and the second end region each preferably occupy, for example, about 5% or less of the area of the IDT electrode 13 . Therefore, the elastic wave that is to be utilized is able to be effectively confined.
  • the areas of the first end region C 11 and the second end region preferably each preferably occupy, for example, at least about 2% of the area of the IDT electrode 13 . In this manner, an unwanted wave is effectively reduced or prevented.
  • the duty of the center region Aa of the IDT electrode 13 gradually decreases in a direction toward the outside in the elastic wave propagation direction in the first end region C 11 and the second end region.
  • the duty at the outermost points in the elastic wave propagation direction is preferably about 0.3, for example.
  • the duty at the outermost points in the elastic wave propagation direction is not limited to this example.
  • FIG. 8 is a diagram illustrating the return loss of the elastic wave device according to the second preferred embodiment.
  • the return loss of the shear horizontal wave is improved to about 1.41 dB.
  • the shear horizontal wave is further reduced.
  • the energy density of a Rayleigh wave tends to be higher in the vicinity of the center of the IDT electrode.
  • the duty increases and the mass of the electrode fingers increases in a direction toward the inside in the elastic wave propagation direction.
  • a Rayleigh wave is less likely to leak.
  • the duty decreases and the mass of the electrode fingers decreases in a direction toward the outside in the elastic wave propagation direction. Therefore, the shear horizontal wave is able to more easily leak.
  • FIG. 9 is a schematic plan view of an elastic wave device according to a third preferred embodiment of the present invention.
  • FIG. 10 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in the third preferred embodiment.
  • an elastic wave device 21 differs from the second preferred embodiment with respect to the configurations of first and second end regions C 11 and C 12 of an IDT electrode 23 . More specifically, the elastic wave device 21 includes a plurality of small duty portions 23 A, which are illustrated as portions with slanted hatching, in the first and second end regions C 11 and C 12 of the IDT electrode 23 .
  • the small duty portions 23 A are portions in which the duty is smaller than the duty in a center region Aa of an inner region D 10 .
  • the elastic wave device 21 has the same or substantially the same configuration as the elastic wave device of the second preferred embodiment.
  • the IDT electrode 23 includes four small duty portions 23 A.
  • the plurality of small duty portions 23 A are disposed at the four corners of the center region Aa of the IDT electrode 23 . More specifically, as illustrated in FIG. 10 , one small duty portion 23 A among the plurality of small duty portions 23 A is disposed so as to include an end portion of the center region Aa on the first low-acoustic-velocity region Ab 1 side in the first end region C 11 .
  • each small duty portion 23 A is disposed so as to include an end portion of the center region Aa on the first low-acoustic-velocity region Ab 1 side or an end portion of the center region Aa on the second low-acoustic-velocity region Ab 2 side in the first and second end regions C 11 and C 12 illustrated in FIG. 9 .
  • each small duty portion 23 A is not particularly limited, and is preferably about 1.4 ⁇ , for example, in the present preferred embodiment.
  • the duty of each small duty portion 23 A is about 0.4 and the duty of the first end region C 11 other than in the plurality of small duty portions 23 A is about 0.5, which is the same or substantially the same as that in the inner region D 10 .
  • the duty of the plurality of small duty portions 23 A is not limited to the above example.
  • FIG. 11 is a diagram illustrating the return loss of the elastic wave device according to the third preferred embodiment.
  • the return loss of the shear horizontal wave is improved to about 1.41 dB.
  • the duty in portions of the center region Aa in the first and second end regions C 11 and C 12 illustrated in FIG. 9 may be made smaller than the duty in the center region Aa of the inner region D 10 .
  • the mass of the electrode fingers in the crossing region A in the first and second end regions C 11 and C 12 is smaller than the mass of the electrode fingers in the crossing region A in the inner region D 10 .
  • a Rayleigh wave is able to be effectively confined and a shear horizontal wave, which is an unwanted wave, is further reduced or prevented.
  • the positions of the plurality of small duty portions 23 A are not limited to the four corners of the center region Aa.
  • the plurality of small duty portions 23 A do not have to include an end portion of the center region Aa on the first low-acoustic-velocity region Ab 1 side and do not have to include an end portion of the center region Aa on the second low-acoustic-velocity region Ab 2 side.
  • the number of locations at which the plurality of small duty portions 23 A are provided is not limited to four locations.
  • the plurality of small duty portions 23 A be disposed in portions of the center region Aa that are close to the first and second low-acoustic-velocity regions Ab 1 and Ab 2 in the first and second end regions C 11 and C 12 .
  • an unwanted wave such as a shear horizontal wave
  • “close to the first and second low-acoustic-velocity regions Ab 1 and Ab 2 ” means within a range of less than or equal to about 1 ⁇ 4 of the length direction dimension of the center region Aa from the end portions of the center region Aa adjacent to the first and second low-acoustic-velocity regions Ab 1 and Ab 2 .
  • the plurality of small duty portions 23 A are more preferably disposed at the four corners of the center region Aa as in the present preferred embodiment. Consequently, an unwanted wave, such as a shear horizontal wave, is more effectively reduced or prevented.
  • FIG. 12 is a schematic plan view of an elastic wave device according to a fourth preferred embodiment of the present invention.
  • FIG. 13 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in the fourth preferred embodiment.
  • an elastic wave device 31 has the same or substantially the same configuration as the elastic wave device of the second preferred embodiment except for the configurations of the first and second end regions C 11 and C 12 .
  • the first and second low-acoustic-velocity regions Ab 1 and Ab 2 are not provided in first and second end regions C 11 and C 12 of an IDT electrode 33 .
  • the duty in the crossing region A in the first and second end regions C 11 and C 12 of the IDT electrode 33 is the same or substantially the same as the duty in the crossing region A in the inner region D 10 .
  • the IDT electrode 33 includes a plurality of first and second dummy electrode fingers 33 a 3 and 33 b 3 in the first and second end regions C 11 and C 12 .
  • First ends of the plurality of first dummy electrode fingers 33 a 3 are connected to a first busbar 3 a 1 and the plurality of first dummy electrode fingers 33 a 3 face a plurality of second electrode fingers 33 b 2 with gaps therebetween.
  • First ends of the plurality of second dummy electrode fingers 33 b 3 are connected to a second busbar 3 b 1 and the plurality of second dummy electrode fingers 33 b 3 face a plurality of first electrode fingers 33 a 2 with gaps therebetween.
  • FIG. 14 is a diagram illustrating the return loss of the elastic wave device according to the fourth preferred embodiment.
  • the return loss of the shear horizontal wave is improved to about 1.61 dB.
  • the IDT electrode 33 does not include a first low-acoustic-velocity region Ab 1 and a second low-acoustic-velocity region in a first end region C 11 , and therefore, the mass of the leading ends of the first and second electrode fingers 33 a 2 and 33 b 2 is small. The same is true for the second end region.
  • the mass of electrode fingers in the crossing region in the first end region C 11 and the second end region is effectively reduced and a shear horizontal wave is effectively allowed to leak.
  • first dummy electrode fingers 33 a 3 and the second dummy electrode fingers are provided outside the crossing region in the length direction.
  • the mass of the electrode fingers in the regions between the first busbar 3 a 1 and the second busbar and the crossing region is able to be made large. Therefore, the shear horizontal wave is able to more easily leak.
  • FIG. 15 is an enlarged plan view of the vicinity of a first end region of the IDT electrode in a fifth preferred embodiment of the present invention.
  • An elastic wave device differs from the fourth preferred embodiment with respect to the positions of gaps between a plurality of first electrode fingers 43 a 2 and a plurality of second dummy electrode fingers and the position of gaps G between a plurality of second electrode fingers 43 b 2 and a plurality of first dummy electrode fingers 43 a 3 in an IDT electrode 43 .
  • the elastic wave device according to the fifth preferred embodiment has the same or substantially the same configuration as the elastic wave device 31 of the fourth preferred embodiment.
  • the gaps G between the plurality of second electrode fingers 43 b 2 and the plurality of first dummy electrode fingers 43 a 3 are superposed with the crossing region in the inner region D 10 when viewed in the elastic wave propagation direction.
  • the gaps between the plurality of first electrode fingers 43 a 2 and the plurality of second dummy electrode fingers are superposed with the crossing region in the inner region D 10 .
  • FIG. 16 is a diagram illustrating the return loss of the elastic wave device according to the fifth preferred embodiment.
  • the return loss of the shear horizontal wave is improved to about 1.54 dB.
  • a shear horizontal wave is further reduced or prevented.
  • FIG. 17 is an enlarged plan view of the vicinity of a first end region of an IDT electrode in a sixth preferred embodiment of the present invention.
  • An elastic wave device differs from the fourth preferred embodiment in that first dummy electrode fingers 53 a 3 and second dummy electrode fingers become increasingly longer in a first end region C 11 and a second end region of an IDT electrode 53 the closer the dummy electrode fingers are to the outside in the elastic wave propagation direction.
  • the elastic wave device according to the sixth preferred embodiment has the same or substantially the same configuration as the elastic wave device 31 of the fourth preferred embodiment.
  • the lengths of the plurality of first dummy electrode fingers 53 a 3 are different from each other in the first end region C 11 and the lengths of the plurality of first dummy electrode fingers 53 a 3 are different from each other in the second end region.
  • the lengths of the plurality of second dummy electrode fingers are different from each other in the first end region C 11 and the lengths of the plurality of second dummy electrode fingers are different from each other in the second end region.
  • the first dummy electrode fingers 53 a 3 and the second dummy electrode fingers become increasingly longer in the first end region C 11 and the second end region the closer the dummy electrode fingers are to the outside in the elastic wave propagation direction.
  • Gaps G between a plurality of second electrode fingers 53 b 2 and the plurality of first dummy electrode fingers 53 a 3 are superposed with a first high-acoustic-velocity region B 1 and the crossing region in the inner region D 10 when viewed in the elastic wave propagation direction.
  • gaps between a plurality of first electrode fingers 53 a 2 and the plurality of second dummy electrode fingers are superposed with a second high-acoustic-velocity region and the crossing region in the inner region D 10 when viewed in the elastic wave propagation direction.
  • the positions of the gaps are not particularly limited, and for example, all of the gaps may be superposed with the crossing region in the inner region D 10 when viewed in the elastic wave propagation direction.
  • FIG. 18 is a diagram illustrating the impedance-frequency characteristics of elastic wave devices of the sixth preferred embodiment of the present invention and a comparative example.
  • FIG. 19 is an enlargement of FIG. 18 .
  • FIG. 20 is a diagram illustrating the return losses of the elastic wave devices according to the sixth preferred embodiment and the comparative example.
  • solid lines represent results of the sixth preferred embodiment and broken lines represent results of the comparative example.
  • Arrows Y in FIGS. 18 and 20 indicate resonant frequencies and arrows Z in FIGS. 18 to 20 indicate anti-resonant frequencies.
  • the comparative example that will be compared with the sixth preferred embodiment is the same as the comparative example compared with the first preferred embodiment described above.
  • the shear horizontal wave is reduced in the present preferred embodiment compared with the comparative example.
  • the return loss other than for the shear horizontal wave, which is an unwanted wave is substantially the same in the sixth preferred embodiment and the comparative example in the frequency band between the resonant frequency and the anti-resonant frequency.
  • the elastic wave that is to be utilized is effectively confined and an unwanted wave is reduced or prevented.
  • preferred embodiments of the present invention may also be applied to an elastic wave device that utilizes a Love wave piston mode.
  • the unwanted wave is a shear vertical wave. Therefore, the return loss of a shear vertical wave, which is an unwanted wave, is improved by an elastic wave device that utilizes a Love wave piston mode and to which preferred embodiments of the present invention have been applied.
  • the elastic wave devices of the above-described preferred embodiments may be used as a duplexer of a high-frequency front end circuit, for example. An example of this will be described hereafter.
  • FIG. 21 is a configuration diagram of a communication device and a high-frequency front end circuit according to a preferred embodiment of the present invention.
  • elements connected to a high-frequency front end circuit 230 such as an antenna element 202 , and an RF signal processing circuit (RFIC) 203 are also illustrated.
  • the high-frequency front end circuit 230 and the RF signal processing circuit 203 define a communication device 240 .
  • the communication device 240 may further include a power source, a CPU, and a display.
  • the high-frequency front end circuit 230 includes a switch 225 , duplexers 201 A and 201 B, filters 231 and 232 , low-noise amplifier circuits 214 and 224 , and power amplifier circuits 234 a, 234 b, 244 a, and 244 b.
  • the high-frequency front end circuit 230 and the communication device 240 illustrated in FIG. 21 are merely examples of a high-frequency front end circuit and a communication device, and the present invention is not limited to these configurations.
  • the duplexer 201 A includes filters 211 and 212 .
  • the duplexer 201 B includes filters 221 and 222 .
  • the duplexers 201 A and 201 B are connected to the antenna element 202 via the switch 225 .
  • the elastic wave devices may be used for the duplexers 201 A and 201 B and the filters 211 , 212 , 221 , and 222 .
  • the above-described elastic wave devices may also be applied to a multiplexer including 3 or more filters, such as a triplexer in which three filters are commonly connected to an antenna element or a hexaplexer in which six filters are commonly connected to an antenna element.
  • the above-described elastic wave devices may be applied to an elastic wave resonator, a filter, a duplexer, and a multiplexer including three or more filters.
  • a multiplexer is not limited to having a configuration that includes both a transmission filter and a reception filter, and may instead have a configuration that includes only a transmission filter or only a reception filter.
  • the switch 225 connects the antenna element 202 and a signal path corresponding to a prescribed band to each other in accordance with a control signal from a control unit (not illustrated), and is, for example, a single pole double throw (SPDT) switch.
  • SPDT single pole double throw
  • the number of signal paths connected to the antenna element 202 is not limited to one and may be a plurality.
  • the high-frequency front end circuit 230 may support carrier aggregation.
  • the low-noise amplifier circuit 214 is a reception amplification circuit that amplifies a high-frequency signal (in this case, a high-frequency reception signal) received via the antenna element 202 , the switch 225 , and the duplexer 201 A and outputs the amplified signal to the RF signal processing circuit 203 .
  • the low-noise amplifier circuit 224 is a reception amplification circuit that amplifies a high-frequency signal (in this case, a high-frequency reception signal) received via the antenna element 202 , the switch 225 , and the duplexer 201 B and outputs the amplified signal to the RF signal processing circuit 203 .
  • the power amplifier circuits 234 a and 234 b are transmission amplification circuits that amplify a high-frequency signal (here, high-frequency transmission signal) output from the RF signal processing circuit 203 and output the amplified high-frequency signal to the antenna element 202 via the duplexer 201 A and the switch 225 .
  • the power amplifier circuits 244 a and 244 b are transmission amplification circuits that amplify a high-frequency signal (here, high-frequency transmission signal) output from the RF signal processing circuit 203 and output the amplified high-frequency signal to the antenna element 202 via the duplexer 201 B and the switch 225 .
  • the RF signal processing circuit 203 subjects a high-frequency reception signal input thereto from the antenna element 202 via a reception signal path to signal processing using down conversion, for example, and outputs a reception signal generated through this signal processing.
  • the RF signal processing circuit 203 subjects an input transmission signal to signal processing using up conversion, for example, and outputs a high-frequency transmission signal generated through this signal processing to the power amplifier circuit 234 a, 234 b, 244 a and 244 b.
  • the RF signal processing circuit 203 is preferably an RFIC, for example.
  • the RF signal processing circuit 203 is connected to a baseband signal processing circuit, for example. In this case, a signal processed by the RF signal processing circuit 203 is input to the baseband signal processing circuit.
  • a signal processed by the baseband signal processing circuit is used for image display as an image signal or for a phone call as an audio signal, for example.
  • the baseband signal processing circuit is included in the communication device 240 .
  • the high-frequency front end circuit 230 may include other circuit elements between the above-described elements.
  • the high-frequency front end circuit 230 may include duplexers according to modifications of the duplexers 201 A and 201 B, instead of the duplexers 201 A and 201 B.
  • the filters 231 and 232 of the communication device 240 are connected between the RF signal processing circuit 203 and the switch 225 without any low-noise amplifier circuits or power amplifier circuits interposed therebetween.
  • the filters 231 and 232 are also connected to the antenna element 202 via the switch 225 similarly to the duplexers 201 A and 201 B.
  • the high-frequency front end circuit 230 and communication device 240 effectively confines an elastic wave that is to be utilized and reduces or prevents an unwanted wave as a result of being equipped with an elastic wave resonator, a filter, a duplexer, a multiplexer including three or more filters, and other suitable components, which are achieved by using an elastic wave device according to a preferred embodiment of the present invention.
  • Elastic wave devices, high-frequency front end circuits, and communication devices according to the present invention have been described above with reference to preferred embodiments and modifications thereof, but other preferred embodiments achieved by combining any of the elements of the above-described preferred embodiments and modifications with one another, modifications obtained by modifying the above-described preferred embodiments in various ways, as conceived by one skilled in the art, without departing from the gist and scope of the present invention, and various devices including a high-frequency front end circuit and a communication device according to preferred embodiments the present invention built thereinto are also included in the present invention.
  • Preferred embodiments of the present invention may be widely used, for example, in communication devices, such as cellular phones, as an elastic wave resonator, a filter, a duplexer, a multiplexer that may be applied to multiband systems, a front end circuit, and a communication device.

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